Never buy a case with a clear side panel, stick it under your desk and never worry about how it looks inside. Or, buy a laptop.
I’ve been building PC’s for over 20 years. Never cared what the insides look like, or the outsides much for that matter, apart from them having a few convenience features on the front panel. As long as the air flow is good and there aren’t any loose cables stopping the fans, especially the CPU fan, which is nothing a few cable ties can’t solve, then there’s really nothing to worry about.
Unless you are really into dressing the insides of your PC, much like some car enthusiasts do with their engines, don’t waste money on useless crud to make it look good. Running a games PC is an expensive enough hobby as it is and given the nature of gaming PC’s, where every 5-6 years you’re replacing a whole load of expensive stuff to keep it current, doing all this interior dressing will just turn your PC into a money hole.
Upgrading your HDD’s to SSD’s is a good move though, but not because it looks good.